Electric phonograph reproducer



INVENTOR III III-I A. A. THOMAS ELECTRIC PHONOGRAPH HEPRODUCER Filed Jan.l8. 1927 Patented May 31, 1927.

UNITED STATES ADQLPH A. THOMAS, OF NEW YORK, N. Y.

ELECTRIC PHONOGRAPH REPRODUCER.

' Application filed January 18, 1927. Serial No. 161,947.

My invention is for an electric phonograph reproducer of novel construction and improved operation. The reproducer of my invention is of the electromagnetic type and comprises a freely movable stylus arm carrying an electromagnetic device arranged in operative relation to the poles of a magnet. I employ no diaphragm to impede the movements of the stylus arm, and the concoil of the reproducer.

sified. A coil spring (or a pair of struction is such that the electromagnetic effect produced by the minute stylus vibrations is intensified by means of a double armature which causes amplified changes in the magnetic flux through the generating I also provide novel means for so pivoting the stylus arm as to eliminate; all looseness and lost motion at the pivot bearing, so thatthe stylus vibra tions are properly transmitted to the electromagnetic device on the stylus arm. As will appear later, my new reproducer is particularly adapted for efficient operation on the new type of long-playing records in which the stylus track runs to several hundred lines to the inch.

In a preferred form of my invention, the Vibratory stylus arm carries at its inner end a pair of spaced armatures. A permanent magnet is so mounted in the reproducer casing that the pole pieces project into the space between the armatures, one of which is surrounded by a generating coil. The' arm'atures provide two parallel magnetic paths for the field flux, so that the vibrations of the stylus arm vary the relative proportion of flux through the armatures. In other words, when the magnetic flux through one of the armatures is increased,

40 the flux through the other armature is simultaneously decreased, whereby the magnetic effect on the generating coil is intensprings) is connected to the stylus arm above the pivot point to exert a constant upward pull on the arm. The effect of this upward pull is two-fold: first, it holds the armatures on the stylus arm in a normal predetermined position relative to the magnetic pole pieces; secondly, it holds the stylus arm firmly in its pivot bearing, which is preferably of the knife-edge type, so that all lost motion is positively eliminated.

The objects and advantages of my invention will be fully understood from a detailed description of the embodiment illustrated in the accompanying drawings, in which Fig. 1 shows an inside face view of an electric phonograph reproducer constructed in accordance with my invention, certain parts being shown in section for clearness;

Fig. 2 is a vertical cross-section approximately on the broken line 22 of Fig. 1, showing a side view of the'mechanism in the casing;

Fig. 3 is a top plan view in section on line 33 of Fig. 1;

Figs. 4 and 5 are diagrammatic plan views showing different positions of the electromagnetic device on the stylus arm in relation to the magnet poles; and

Fig. 6 is an enlarged fragmentary view in cross-section showing a construction for altering the line of pull and regulating the degree of tension exerted by the spring or sprin s attached to the stylus arm.

Before beginning a detailed description of the drawings, I Want to explain that the various views have been purposely drawn on an exaggerated scale in order to make the construction and operation of the reproducer as clear as possible. For this purpose the various parts have been spread out in position and dimensions considerably more than is necessary in actual practice. It will therefore be understood that the figures about to be described are not to be considered 'inthe nature of shop drawings.

The parts that go to make up the electric reproducer are mounted in a casing (I of suitable construction and design. In the presentinstance, the casing comprises a central body section 10 having the general shape of a pear or electric light bulb, a front plate 11 and a rear plate 12. These parts are preferably made of light sheet metal, such as aluminum, brass or other nonmagnetic material, and are secured together by screws 13 or in any other practical way. The back plate 12 has a hub 14 for attaching the casing to a supporting arm.

In casing C is rigidly mounted a permanent steel magnet M substantially U-shapcd and terminating in a pair of pole pieces 15. As shown in Figs. land 3, the pole pieces 15 are arranged substantially at the center of the casing, and for that purpose the limbs of the magnet are bent laterally at 16. The magnet is mounted against one of the slanting walls of the pear-shaped section and is firmly held in position by screws 16' or otherwise. It will be ob served that the permanent magnet M is so shaped as to provide a magnetic field of maximum length in a small casing.

The bottom; plate 17 of casing C carries a knife-edge bearing consisting of a pair of 23. If desired, the bearing members 18 may be mounted on stylus arm 22 and the knife- 4 edge 21 attached to the bottom of the casneedle 24 for lateral-cut records.

ing-this being a mere reversal of the construction shown. In the present embodiment, the stylus arm 22 is shown as a needle arm adapted to support a record-pltiymg t 15 clear, however, that my invention is equally well adapted for playing vertical-cut records of the Pathe type and the Edison type,

by merely making such changes as are obvious to anyone conversant wlth the art.

To the inner end of stylus arm 22 is secured a vice E is secured to the inner end wise.

ends of a pair of coil springs 31.

' the coil opening an electromagnetic device indicated as a whole by E. This device comprises a pair of armatures 25 and 26 and a generating coil 27. The armatures are preferably small bars of soft iron or other metal of high magnetic permeability, and they are connected together as a single I1gl d frame by means of non-magnetic end pieces 28, which maybe of aluminum or other light material. The coil 27 surrounds the armature 25 and is shown as being supported thereby. In the broader aspect of.my 1n- VeDtiOIi; 'the' coil may be mounted 1n stationary position, it being only necessary that be large enough to allow free movement of the associated armature bar. Although I have shown but one coil, it is evident that each armature may have a generatingcoil. The electromagnetic deof stylus arm 22 in any practical way, as by means of a clip 29 secured centrally to the armature bar 26 by screws, soldering, or other- The stylus arm 22 is provided at a cer- .tain distance above its pivot bearing with a cross-pin 30, to which are fixed the lower Onl one spring need be used, but" two are pre erable, one on each side of the arm, for securing better mechanical balance. The upper ends of springs 31 are attached to across-pin 32 supported from the top of the casing by means of a screw-threaded shank 33, which is adjustably mounted in a bearing sleeve 34 extending through a transverse slot 35 in the casing. The sleeve slot 35 and then clamped down in adjusted position. This lateral adjustment of crosspin 32 regulates the line or direction of pull of the springs 31 on the stylusarm 22, whereby the normal position of the armatures 25 and 26 relative to the pole pieces 15 may le regulated as desired. A nut.39 on the screw-threaded shank 33 permits the vertical adjustment of cross-pin 32 to regulate the normal tension of rings 31.

Any suitable means may %e used to pre vent turning of the shank 33 during the adustment of nut 39. In Fig. 6, the shank 33 is provided with a flat or square portion 40 fitting snugly between a pair of shoulders 41 onthe lower end of sleeve 34. The shoulders 41 prevent turning of the shank 33 without interfering with its vertical movement. In order to keep the transverse slot 35 closed at all times, a thin cover-plate 42 may be inserted between the casing and the nut 37. This cover-plate is provided with an opening through which the supporting sleeve 34 extends, and is of such length that it covers the slot 35 in all positions of the sleeve.

' The operation of the reproducer above described will be clear to those skilled in the art, but I may summarize it as follows: Let us suppose that the parts are in normal position, as shown in Fig. 3, with the pole pieces 15 substantially midway of the spaced armatures 25 and 26. The magnetic field flux normally divides about evenly between the two armatures, which constitute parallel magnetic paths. It is not, however, essential that the armatures are normally held at the same distance from the magnet poles. When the stylus arm 22 swings toward the left, as indicated by arrow a in Fig. 1, armature 26 moves toward the pole pieces, and armature 25 moves away from the pole pieces, as roughly indicated in Fig. 4; Most of the magnetic flux will now pass through armature26, and the flux through coil E is correspondingly decreased, whereb electric impulses are generated in the coi. When the needle arm swings toward the right, as indicated by arrow 6 in Fig. 1, the relation of the armatures to the magnetic poles is as indicated in Fig. 5; The magnetidflux now passes for the most part through armature 25 and coil 27. If we assume the positions of the electromagnetic device E in Figs. 4 and 5 as the two extreme positions, there will be an almost infinite number of intermediate positions for varying the flux In fact, they are barely detectable by the naked eye. Nevertheless, these delicate movements are sufficient to induce current impulses in coil 27, and these impulses are utilized in any practical way to operate.

loudspeaker mechanism. This will be understood by those familiar with the art Without the need of additional description or illustration. a

The springs 31 continuously exert an upward pull on the knife-edge 21, and thus firmly hold the same at all times in the apex of bearing members 18. In this way there is no possibility of lost motion in any position of-the stylus arm during recordplaying operation, and the arm moves with practically no friction. As seen in Fig. 1,

the pivot point of stylus arm 22 is so arranged that the stylus vibrations are transmitted in amplified ratio to the electro-magnetic device E at the inner end of the arm. These two factorsthe elimination of lost motion at the pivot bearing of the stylus arm and the amplified transmission of the stylus vibrations to the inner end of the armare of particular importance in playing the new type records where the stylus track is almost microscopic and where the maximum vibrations of the stylirs point may be less than 0.001 inch.

The unit E is made so light that it has no appreciable inertia. The spring or springs 31 impose the right amount of load on the stylus arm for the best reproduction. This load, or mechanical impedance, may be made very small, so that the stylus point is sure to follow the most minute sinuations of the record groove without injury to the frail walls thereof. Since the armatures 25 and 26 are on opposite sides of the magnet poles, the normal tendency of the magnetic field is to assist the springs 31 in holding the stylus arm balanced. Attention is called to the fact that the flux variations produced by the movements of arm 22 Toccur only in the armatures 25 and 26 and not in the steel body of the magnet. This addsto the sensitiveness of the instrument, for the permeable iron of the armatures offers very little resistance to changes in magnetic flux.

Although I have shown and described a specific construction of reproducer, I want it understood that I have done so merely to explain my invention, and not by way of restriction or limitation thereof. It is doubtless possible to make changes and alterations without departing from the scope of the invention as defined in the following claims. I

I claim as my invention:

1. An electric phonograph reproducer comprising a vibratory stylus arm carrying a pair of magnetic members arranged to provide parallel magnetic paths, a magnet having pole pieces so arranged witlrrespect to said magnetic members that vibratory movements of said arm cause simultaneous flux variations in said members, and a coil influenced by said flux variations.

2. An electric phonograph reproducer comprising a vibratory stylus arm carrying a pair of spaced armatures arranged substantially parallel, a coil surrounding one of said armatures, and a magnet havin pole pieces so arranged with respect to said armatures that the vibrations of said arm increase the magnetic flux through one armature and simultaneously decrease the flux through the other armature, whereby electric impulses are induced in said coil.

3. An electric phonograph reproducer comprising a vibratory stylus arm carrying at its free end anelectromagnetic unit consisting of two magnetic members and a coil on one of said members, said members being magnetically separated, and means for providing a substantially constant magnetic field to produce flux variations through said members during the movements of said arm.

4. An electric phonograph reproducer' comprising a vibratory sty'lus arm carrying a pair of spaced armature bars, a coil surrounding one of said bars, a magnet having pole pieces projecting into the space be tween said bars, which thus provide two parallel ma netic paths for the field flux, so that the vi rations of said arm vary the relative proportion of flux through said armature bars and thereby induce electric impulses in said coil, and elastic means for normally holding said arm and bars in predetermined position.

5. An electric phonograph reproducer comprising a pivoted stylus arm carrying at its free end a pair of spaced armature bars which vibrate in amplified relation to the stylus movements, a coil on one of said bars, a magnet having pole pieces projecting into the space between said bars, which thus provide two parallel magnetic paths for the field flux, so that the vibrations of said stylus arm vary the relative proportion of flux through said bars and thereby induce electric impulses in said .coil, and spring means connected to said arm for normally holding the two armature bars at approximately equal distance from said pole pieces.

6. In an electric phonograph reproducer, a casing provided with a pivot bearing at its lower end, a stylus arm mounted in said pivot bearing for vibratory movement, a spring connected at one end to said arm and holdin edge bearing in rm contact with each other,

arm above its pivot and at the other end to said casing for holding said arm firmly in said bearing during the vibrations thereof, said spring exerting an upward pull on said varm and thus. normally holding the same in predetermined position, and electric reproducing mechanism controlled by said arm in accordance with the movements of the stylus. v

'7. In an electric phonograph reproducer,

a vibratory stylus arm, a tensioned coil spring connected to said arm for exerting a a casing provided with a knife-edge bearing, a vibratory stylus arm'pivoted in said bearing, a tensioned coil spring connected to said armv above its piyot point for constantly exerting an upward pull on said the parts of said knifesaid spring also holding the stylus. arm in normal predetermined. position, and electric reproducing mechanism controlled 'by said arm in accordance with the movements of the stylus.

9. In an electric phonograph reproduoer, a I

held in predetermined position by said.

sprin means.

1O. In an electric phonograph reproducer, a casin provided at its lower end with a knife-edge bearing, a vibratory stylus arm pivoted 1n said bearing, a pair of tensioned coil springs secured to said arm above said bearing to exert a constant upward pull on said arm, whereby said springs hold the bearing parts together to prevent 10st motion during the vibrations of said arm and also act to restore said arm to predetermined normal position, and electric reproducing mechanism controlled by the movements said arm.

ADOLPH A. THOMAS. 

